A simulation-based optimization approach for analyzing ambulance diversion in emergency medical systems: application to an urban area of Rome

This paper deals with an important issue in Emergency Medical Systems, namely the overcrowding of the Emergency Departments (EDs). In particular, we propose a novel model based on Discrete Event Simulation (DES) for studying the Ambulance Diversion (AD), the strategy of temporarily redirect patients incoming by ambulance to another nearby ED when the receiving ED is overloaded. While AD can provide temporary relief to overcrowded EDs, it can be associated with significant risks and some healthcare organizations restrict or prohibit AD. On the other hand, many healthcare systems promote AD as collaboration between EDs, enabling load balancing across facilities, in the perspective of resource pooling policy in a ED network. We analyze the effects of different AD strategies in terms of timely patient care, outcomes and healthcare costs, using the Simulation-Based Optimization (SBO) approach. In particular, we adopt an appropriate DES model for reproducing the operation of the ED network. Moreover, in our approach, an optimal resource allocation problem consisting of a bi-objective SBO problem is considered. The aim is to minimize the non-value added time spent by patients and the overall cost incurred by the ED network. In this way, for each ED and AD policy, a set of optimal points belonging to the Pareto frontier, representing an optimal resource allocation, can be obtained. Then, a real case study consisting of five large EDs in the urban area of Rome, Italy has been considered. The DES model of the ED network has been implemented using ARENA simulation software. The optimization phase adopted in the SBO approach is based on a recently proposed and publicly available multiobjective mixed-integer (constrained) derivative-free method.